Self-contained die cushion with air saver



United States Patent 3,511,491 SELF-CONTAINED DIE CUSHION WITH AIR SAVERDerald Henry Kraft, Canton, Ohio, assiguor to E. W.

Bliss Company, Canton, Ohio, a corporation of Delaware Filed July 13,1967, Ser. No. 653,116 Int. Cl. BZld 24/02; F16f 9/04, 13/00 U.S. Cl.2671 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relatesto the art of self-contained die cushions, and more particularly to aself-contained die cushion having an air saver or reservoir incorporatedtherewith.

This invention is particularly applicable for use in a power presswherein depending rods are used to support a hold-down ring of a drawingdie, and it will be described with particular reference thereto;however, it is appreciated that the invention has much broaderapplications and may be used in various other environments wherein a diecushion is required.

Many dies used Within power presses incorporated hold-down rings orother auxiliary elements which are controlled, to a certain extent, by adie cushion located below the bolster of the power press. These diecushions take a variety of forms; however, the most common die cushionincludes two telescoped sleeves with end walls defining an internalcushion chamber filled with a compressible fluid which biases the uppersleeve in an upwardly direction. A plurality of rods extendingdownwardly from the die within the press rests upon the upper sleeve,generally known as a pressure pad. These rods coact with movableelements within the die so that the pressure pad is forced downwardly bythe rods during the downward stroke of the press. The downward movementof the upper sleeve or pressure pad compresses the fluid within thecushion chamber so that the rods are forced in an upward direction bythe pressure pad during the upward stroke of the power press. The volumeof air, or other compressible fluid, within the chamber of the diecushion is quite large to provide the necessary biasing action for thedownwardly extending rods. This presents a substantial difficulty.

When a die is to be repaired or replaced, the die cushion must bedropped into an inoperative position. One common way of accomplishingthis is to exhaust most of the fluid from the chamber of the diecushion. This requires a substantial amount of time to exhaust and thenreplace the large volume of fluid Within the die cushion. In an effectto reduce the time for exhausting and filling the chamber of the diecushion, relatively large supply hoses have been used. These areexpensive, and they do not substantially reduce the total time requiredto drop the die cushion into its inoperative position and then raise thedie cushion into its operative position. To overcome the disadvantagesof this particular arrangement, it has been suggested that a fluidreservoir should be mounted adjacent the die cushion with a valvebetween the reservoir and the cushion. When the die cushion is to bedropped, the valve is opened to store fluid Within the reservoir. Thevalve was then closed so 3,511,491 Patented May 12, 1970 that the fluidwould remain in the reservoir. To raise the die cushion, the valve wasagain opened which allowed flow of fluid back to the die cushion. Thisagain involved complex and expensive mechanical arrangements toaccomplish the operation of the die cushion.

The structure explained above has been modified to provide the reservoirand valve Within the die cushion itself. When this is done, the pipingbetween the reservoir and the die cushion chamber is eliminated;however, certain inherent disadvantages are built in. The valve betweenthe reservoir and die cushion must be operated, mechanically, from aposition outside of the die cushion. Thus, a rod or other valveoperating means must be provided internally of the die cushion. Also,when the valve becomes defective, the die cushion must be taken apartand repaired. By providing internal valving within the die cushion, itis diflicult to provide hydraulic snubbers or hydraulic hold-downs whichare generally used in the operation of a die cushion. A hydraulicsnubber is used to control the upward movement of the die cushion sothat it is somewhat out of phase with the upward stroke of the powerpress. The hydraulic hold-down is utilized to lock the die cushion in adownward position when the die cushion is not to be used. v

The disadvantages of the prior die cushions are com pletely overcome bythe present invention which is a completely new concept to the art ofdie cushions and includes a simplified structure which will allowmovement of the die cushion between its upward operative position andits lower inoperative position.

In accordance with the present invention, there is provided animprovement in a self-contained die cushion, comprising a movable,operative member and fluid means for biasing the member in a givendirection for movement between points a and b wherein the fluid meansincludes defining a cushion chamber filled with a compressible fluid andhaving a total volume V or V when the member is at point a and a totalvolume V or V when the member is at point b, V being greater than V Alsoprovided is a means defining a sealed fluid filled reservoir within thechamber with at least one movable exterior wall, this reservoir havingvariable volume V which forms part of the volume of the chamber and is,at all times, substantially less than volume V Also provided are meansfor exhausting fluid from the chamber while the reservoir remains filledwith fluid. In this manner, the die cushion may be dropped by exhaustingonly a portion of the cushion chamber. During normal operation of thedie cushion, the filled reservoir within the chamber coacts through themovable external wall to provide a continuous, relatively large volumeof air against which the die cushion operates. The improvement to thedevice defined above is the formation of the sealed fluid chamber as aflexible diaphragm which defines colume V and a fixed rigid wall meansfor limiting the movement of the diaphragm in the volume expandingdirection.

The primary object of the present invention is the provision of aself-c0ntained die cushion which is inexpensive to produce, usable inexisting presses without modification and easily and rapidly droppedinto the inoperative position and raised into the operative positionwith a minimum of fluid.

Another object of the present invention is the provision of aself-contained die cushion which requires a lesser amount of air, orfluid, to shift from the inoperative position to the operative position.

Yet another object of the present invention is the provision of. aself-contained die cushion which incorporates two separate, isolatedfluid compartments in the cushion chamber, both of which coact toprovide the biasing action of the cushion and one of which is exhaustedto drop 3 the cushion into its inoperative position, which chamber isdefined by a flexible diaphragm.

These and other objects and advantages will become apparent from thefollowing description used to illustrate preferred embodiments of theinvention as read in connection with the accompanying drawings in which:

FIG. 1 is a partial, cross-sectional view illustrating, somewhatschematically, the structure to which this invention is an improvement.

FIG. 2 is a partial, cross-sectional view illustrating a modification ofthe structure as shown in FIG. 1 with one aspect of the presentinvention shown;

FIGS. 3-5 are partial, cross-sectional views illustrating certainmodifications of the structures shown in FIGS. 1 and 2;

FIG. 6 is a cross-sectional view illustrating the preferred embodimentof the main aspect of the present invention;

FIG. 7 is a partial, cross-sectional view illustrating the operationalcharacteristics of the embodiment of the invention illustrated in FIG.6;

FIG. 8 is an enlarged, cross-sectional view illustrating still a furthermodification of the present invention; and,

FIG. 9 is a partial cross-sectional view showing the operatingcharacteristics of the embodiment of the invention illustrated in FIG.8.

Referring now to the drawings, wherein the showings are for the purposeof illustrating preferred embodiments of the invention only and not forthe purpose of limiting the same, :FIG. 1 shows a self-contained diecushion A which is mounted on a support plate B attached to the underframe of a press (not shown) by a plurality of rods 10, 12. The generaloperation of the die cushion is well known in the power press art;therefore, further discussion of the press itself, except with regard tothe general operation of the die cushion, is not required.

Self-contained die cushion A includes a fixed sleeve 20 having a lowerflange 22 secured onto a lower end wall 24 by a plurality ofcircumferentially spaced bolts 26. In like manner, bolts 28 secure thewall 24 onto the support plate B. An appropriate seal, such as O-ringseal 30, is provided between flange 22 and wall 24. Sleeve 20 alsoincludes an outer bearing surface 32 which terminates at a recess 34 toform an abutment 36. Adjacent the upper portion of sleeve 20 there isprovided appropriate seal 38, for a purpose which will be apparent fromthe further description of this embodiment. Also at the upper end ofsleeve 20 is a relatively large opening 40 defined by a flange 42 havinga lower abutment 44.

Reciprocally and telescopically received on sleeve 20 is a movablesleeve, or pressure pad, 50 which forms the operative member of the diecushion, in a manner to be described later. Sleeve 50 has an upper endwall 52, an inner mounting surface 54 slidably received on surface 32,and a lower stop 56 adapted to coact with abutment 36 to preventwithdrawal of sleeve 50 from sleeve 20. End wall 52 is provided with anupwardly facing, top surface 58 which is adapted to contact the lowerend of operating rods 60. These rods are connected to various elementswithin the die mounted upon the bolster of a power press, in a mannerwell known in power press art.

Sleeves 20, 50 combine to form the total air chamber, hereinafterreferred to as the internal cushion chamber 70 which is filled withpressurized fluid from an input line 72. Line 72 includes a branch 74communicated with the lower portion of chamber 70 and a branch 76communicated with the upper portion of chamber 70. This lastmentionedcommunication is through a passage 80, line 82,- check valve 84, andcontrol valve 86. The valve 86 is positioned as indicated in FIG. 1. Theupper portion of chamber 70 is communicated with pressurized fluid frominput line 72. Check valve 84 prevents fluid flow from the upper portionof chamber 70 to supply line. In a like manner, a check valve can beprovided in branch 74. To exhaust the upper portion of chamber 70, valve86 could be manually actuated to connect line 82 with exhaust line 88.As so far described, the self-contained die cushion does not differsubstantially from normal die cushions, except for flange 44 and certainaspects of the fluid inlet system.

In operation, rods 60 are connected onto certain elements within thedie, such as knock-out pins or a drawing ring. As the power press movesdownwardly to close the die, rods 60 push sleeve 50 downwardly from anupper point a to a lower point b. This is done against the fluid bias ofcushion chamber 70. As the power press moves upwardly, the fluidpressure within chamber 70 forces sleeve 50 back to its initial upperpoint a. The rods 60 are raised and perform the necessary functionwithin the die, in accordance with the particular element beingcontrolled by the rods. This procedure is repeated in each cycle of thepower press. The total volume of fluid within chamber 70 is V- or V whenthe sleeve 50 is at point a. In like manner, the total volume of chamber70 is V or V when the sleeve 50 is at point 12. Consequently, thedifference in volume during the normal operation of die cushion A is Vminus V Sleeve 20 is provided with a vertically movable wall 90, in theform of a piston having a top 92, a skirt 94, and a peripheral seal 96.Spring 98 biases the piston 90 in an upward direction. The movable wall90 divides the total fluid volume of chamber 70 into an upper portion100 and a lower portion 102. The lower portion has a variable volume Vwhich is dependent upon the position of the wall 90 with respect tosleeve 20. The volume V is always substantially less than total volume Vand volume V is also substantially less than total volume V-;;. Pistonor wall 90 forms two isolated, separate portions in chamber 70. This hasan extremely beneficial result which will be described later.

In operation, during normal function of the die cushion A, sleeve 50moves between points a and b. This causes the fluid within chamberportions 100, 102 to be alternately compressed and expanded. During thisoperation, piston or wall 90 oscillates within sleeve 20, and it doesnot substantially affect the operation of the die cushion. There is nointer-fluid flow between portions 100, 102 of the embodiment shown inFIG. 1. The interrelationship between these portions can be described asbeing mutual fluid pressure relationship or inter-force transmittingrelationship. In other words, the air or other fluid within portions100, 102 functions in a manner generally simulating a situation where nowall or piston 90 is used.

When a die within the power press is to be repaired or replaced, the diecushion must be dropped. This is accomplished by exhausting portion 100through valve 86. As the pressure within portion 100 is reduced, thepressure within portion 102 drives wall or piston 90 upwardly againstabutment 44. -In this manner, all of the fluid within portion 102 isretained within the die cushion, and it need not be replaced when thedie cushion is again activated. To activate the die cushion, valve 86 ismoved to the position illustrated in FIG. 1, and fluid pressure frominput line 72 is forced through passage into portion 100. Thisimmediately pumps up the die cushion into its operative position.

It can be appreciated that only the volume of air necessary to fillchamber portion 100 is required to activate the die cushion, althoughthe die cushion operates against the complete volume of fluid withinboth portions 100, 102. Since only a small volume of air is needed toactivate the die cushion, the time required to activate and deactivatethe die cushion is substantially reduced. Wall provides a positive sealbetween the fluid in portion and portion 102 when the die cushion is inits inactive position. There is no possibility of an inrush of air toportion 100 which would cause the die cushion to inadvertently move toits outward position while the die is being changed or repaired. Thestructure shown in FIG. 1 does not require complicated valving withinthe die cushion itself or other complicated mechanisms to provide aninternal reservoir of fluid which is not periodically exhausted andreplaced when the die cushion is to be dropped and again actuated. Therelatively small volume of air needed to activate the die cushion coactswith the air remaining within portion 102 to provide normal operation ofthe die cushion.

Referring now to FIG. 2, a certain aspect of the present invention isshown wherein sleeve 20 is secured onto a mounting plate 110 having arelatively large opening 112. A somewhat standard hydraulic lockingdevice 120 is secured to the lower end of plate 110. The control rod 122for the hydraulic locking device extends from end wall 52 of sleeve 50,through an opening 124 in piston 90 having a bearing seal 126, andthrough opening 130 of the device 120. The usual operating piston 134 isprovided within the hydraulic locking device 120 and hydraulic fluid 136 is provided within the lower portion of sleeve 20 and is communicatedby line 138 to the interior of the locking device 120. By utilizing thepiston 90, the selfcontained die cushion may be provided with thisstandard hydraulic locking device without substantial modification ofthe die cushion. This is a substantial advantage because certaininstallations require the hydraulic locking device to hold the diecushion in an inoperative position during portions of a cycle or duringvarious operations of the press itself.

Referring now to FIG. 3, a modification of the piston 90 is illustrated.Piston 90a is provided with an outer peripheral seal 140 and spaced vaneseals 142, 144 for passage of rod 122. A spring 146 surrounds the rod122 and biases the piston 90a in an upward direction.

Referring now to FIG. 4, a hydraulic snubber 150 is provided below theend wall 24 of sleeve 20. The control rod 122 having a lower piston 134is connected to the end wall 52, as shown in FIG. 2. The hydraulicsnubber 150 includes a control valving assembly 152 so that the movementof sleeve 50 in an upward direction after being first moved downwardlyis controlled. This prevents abrupt upward movement of rods 60 duringthe operation of the die cushion shown in FIGS. 1 and 2. This embodimentof the invention illustrates the ease by which a standard hydraulicsnubber may be incorporated within a die cushion constructed inaccordance with the present invention.

Referring now to FIG. 5, a fixed sleeve 160 includes an inwardlyextending flange 162 having a peripheral, lower seal 1 64. Reciprocalpiston 170 includes a downwardly extending rod 172 which is receivedwithin a bore 174 having a spring 176 held in place by a plate 178. Thepiston 170 is provided with a plurality of peripheral grooves 180 whichallow communication between the upper fluid portion 182 and the lowerfluid portion 184 within sleeve 160. The peripheral grooves 180 aresealed when piston 170 is in its uppermost position against seal 164.Consequently, when a die cushion including this structure is to bedropped, fluid portion 182 and the interior of the upper sleeve 50, notshown is exhausted. This causes a rapid increase in the pressuredifferential across piston 170. This diiferential 'forces the piston inan upward direction to seal against seal 164. The pressure within fluidportion 184 maintains the piston in its sealed condition until fluidpressure is again introduced into the portion 182. This embodiment ofthe invention functions somewhat diflerently from the previouslymentioned embodiments in that actual fluid communication is providedbetween the upper and lower fluid portions defined by the movable piston170.

Attention is now directed to FIGS. 6 and 7. These figures illustrate theprimary aspect of the present invention wherein a fixed sleeve 1190 hasan upper opening 192 which is covered by a flexible diaphragm 194. Abovethe diaphragm there is secured, onto the sleeve 190, a rigid perforatedplate 196. The diaphragm divides the 6 fixed sleeve into two separate,sealed, isolated fluid portions 200, 202. In FIG. '6, portion 202 issubstantially zero. The diaphragm 194 flexes downwardly as sleeve 50 isforced downwardly by rods '60 and flexes upwardly as the rods 60 areallowed to move upwardly.

When portion 202 in the interior of sleeve 50 is exhausted, fluid withinportion 200 is retained as diaphragm 194 moves upwardly into contactwith plate 196, as shown in FIG. 6. A similar device is illustrated inFIGS. 8 and 9. In this embodiment, a fixed sleeve 210 is provided with asupport spider 212 onto which is mounted a rod guide 214. Rod 122, for ahydraulic snubber, or locking device, is received within the guide bybearing seals 216, 218. Since the central guide is used, an annularopening 220 is provided at the upper portion of the fixed sleeve, andthis opening is sealed by an annular diaphragm 222. Above the disphragmthere is secured an annular perforated plate 224 which limits the upwardextent or deflection of diaphragm 222. The diaphragm divides theinterior of the fixed sleeve into separate, isolated, sealed portions230, 232 with portion 232 being substantially zero when the diaphragm isin its upwardmost position, as shown in FIG. 8.

The present invention has been described in connection with certainstructural embodiments; however, many modifications of these embodimentscan be made.

Having thus defined my invention, I claim:

1. In a self-contained die cushion comprising a first sleeve, a secondsleeve telescopically and reciprocally received on said first sleeve,said sleeves having end walls and combining to define a cushion chamberfor a compressible fluid between said end walls, said second sleevebeing biased upwardly by the fluid in said cushion chamber duringoperation of said die cushion and being dropped to an inoperativeposition when said die cushion is to be inoperative, means for dividingsaid chamber into separate, isolated first and second fluid chamberportions, means for limiting the expanded volume of said first portionto an extent incapable of preventing said second sleeve from dropping toan inoperative position upon exhausting of said second portion, andmeans for exhausting said second portion to drop said second sleeve tothe inoperative position, the improvement comprising: a spring means forbiasing said movable wall in an upward direction.

2. The improvement as defined in claim 1 wherein said movable wallincludes a downwardly extending rod and said end wall of said firstsleeve includes a passage for journaling said rod.

3. The improvement as defined in claim 2 including a spring means insaid passage for biasing said rod and said wall in an upward direction.

4. In a self-contained die cushion comprising a first sleeve, a secondsleeve telescopically and reciprocally received on said first sleeve,said sleeves having end walls and combining to define a cushion chamberfor a compressible fluid between said end walls, said second sleevebeing biased upwardly by the fluid in said cushion chamber duringoperation of said die cushion and being dropped to an inoperativeposition when said die cushion is to be inoperative, means for dividingsaid chamber into separate, isolated first and second fluid chamberportions, means for limiting the expanded volume of said first portionto an extent incapable of preventing said second sleeve from dropping toan inoperative position upon exhausting of said second portion, andmeans for exhausting said second portion to drop said second sleeve tothe inoperative position, the improvement comprising: said first sleevebeing mounted on a support plate and including a rod extending from theend wall of said second sleeve, through said chamber, through saiddividing means, and through said plate, and means on said plate oppositesaid sleeves for controlling the rate of movement of said second sleevein, at least, the upward direction.

5. The improvement as defined in claim 4 wherein said 7 8 dividing meansis a rigid wall reciprocally mounted in References Cited said firstsleeve and said rod extends through said rigid UNITED STATES PATENTSwall.

6. The improvement as defined in claim 4 wherein said 3,410,202 11/1968chrubaslk 100264 dividing means is a rigid wall reciprocally mounted in10331552 5/1962 Ogden 2671 0 3,375,001 3/1968 Hennells 2671 said firstsleeve and said rigid wall having a central bearing bore, said bearingbore reciprocally mounting said rigid wan Onto said rod. ARTHUR L. LAPOINT, Primary Examiner

